In a medium saucepan place the olive oil and heat it on medium high until it is hot. Add the onions and saute them for 2 to 3 minutes, or until they are tender. Add the pancetta, bratwurst, and chicken. Saute the ingredients for 5 minutes. Add the soaked beans, tomatoes, chicken stock, bay leaves, and thyme. Simmer the beans for 1-1/2 hours, or until they are tender. Add the salt and the pepper, and stir them in. Remove the bay leaves and strain off the liquid (reserve it for a future use).